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PDF MCP7940M Data sheet ( Hoja de datos )
| Número de pieza | MCP7940M | |
| Descripción | Real-Time Clock/Calendar | |
| Fabricantes | Microchip | |
| Logotipo |  |
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MCP7940M
Low-Cost I2C™ Real-Time Clock/Calendar with SRAM
Timekeeping Features:
• Real-Time Clock/Calendar (RTCC):
- Hours, Minutes, Seconds, Day of Week, Day,
Month, Year
- Leap year compensated to 2399
- 12/24 hour modes
• Oscillator for 32.768 kHz Crystals:
- Optimized for 6-9 pF crystals
• On-Chip Digital Trimming/Calibration:
- ±1 PPM resolution
- ±129 PPM range
• Dual Programmable Alarms
• Versatile Output Pin:
- Clock output with selectable frequency
- Alarm output
- General purpose output
Low-Power Features:
• Wide Voltage Range:
- Operating voltage range of 1.8V to 5.5V
• Low Typical Timekeeping Current:
- Operating from VCC: 1.2 µA at 3.3V
User Memory:
• 64-byte SRAM
Operating Ranges:
• 2-Wire Serial Interface, I2C™ Compatible
- I2C clock rate up to 400 kHz
• Temperature Range:
- Industrial (I): -40°C to +85°C
Packages:
• 8-Lead SOIC, MSOP, TSSOP, PDIP and 2x3
TDFN
General Description:
The MCP7940M Real-Time Clock/Calendar (RTCC)
tracks time using internal counters for hours, minutes,
seconds, days, months, years, and day of week.
Alarms can be configured on all counters up to and
including months. For usage and configuration, the
MCP7940M supports I2C communications up to 400
kHz.
The open-drain, multi-functional output can be
configured to assert on an alarm match, to output a
selectable frequency square wave, or as a general
purpose output.
The MCP7940M is designed to operate using a 32.768
kHz tuning fork crystal with external crystal load
capacitors. On-chip digital trimming can be used to
adjust for frequency variance caused by crystal
tolerance and temperature.
Package Types
SOIC, MSOP, TSSOP, PDIP
X1 1
X2 2
NC 3
VSS 4
8 VCC
7 MFP
6 SCL
5 SDA
TDFN
X1 1
X2 2
NC 3
VSS 4
8 VCC
7 MFP
6 SCL
5 SDA
2012-2014 Microchip Technology Inc.
DS20002292B-page 1
1 page  
FIGURE 1-3:
I2C BUS TIMING DATA
5
2
SCL
SDA
In
7
6
13
3
8
SDA
Out
11
9
D3
MCP7940M
4
10
12
2012-2014 Microchip Technology Inc.
DS20002292B-page 5
5 Page 
4.2 Oscillator Configuration
The MCP7940M can be operated in two different oscil-
lator configurations: using an external crystal or using
an external clock input.
4.2.1 EXTERNAL CRYSTAL
The crystal oscillator circuit on the MCP7940M is
designed to operate with a standard 32.768 kHz tuning
fork crystal and matching external load capacitors. By
using external load capacitors, the MCP7940M allows
for a wide selection of crystals. Suitable crystals have a
load capacitance (CL) of 6-9 pF. Crystals with a load
capacitance of 12.5 pF are not recommended.
Figure 4-2 shows the pin connections when using an
external crystal.
FIGURE 4-2:
CRYSTAL OPERATION
MCP7940M
X1
CX1
Quartz
Crystal
To Internal
Logic
ST
CX2 X2
Note 1: The ST bit must be set to enable the
crystal oscillator circuit.
2: Always verify oscillator performance over
the voltage and temperature range that is
expected for the application.
4.2.1.1 Choosing Load Capacitors
CL is the effective load capacitance as seen by the
crystal, and includes the physical load capacitors, pin
capacitance, and stray board capacitance. Equation 4-1
can be used to calculate CL.
CX1 and CX2 are the external load capacitors. They
must be chosen to match the selected crystal’s speci-
fied load capacitance.
Note:
If the load capacitance is not correctly
matched to the chosen crystal’s specified
value, the crystal may give a frequency
outside of the crystal manufacturer’s
specifications.
MCP7940M
EQUATION 4-1: LOAD CAPACITANCE
CALCULATION
CL = -CC----XX---11----+-----CC----X-X--2-2 + CSTRAY
Where:
CL = Effective load capacitance
CX1 = Capacitor value on X1 + COSC
CX2 = Capacitor value on X2 + COSC
CSTRAY = PCB stray capacitance
4.2.1.2 Layout Considerations
The oscillator circuit should be placed on the same
side of the board as the device. Place the oscillator
circuit close to the respective oscillator pins. The load
capacitors should be placed next to the oscillator
itself, on the same side of the board.
Use a grounded copper pour around the oscillator cir-
cuit to isolate it from surrounding circuits. The
grounded copper pour should be routed directly to VSS.
Do not run any signal traces or power traces inside the
ground pour. Also, if using a two-sided board, avoid any
traces on the other side of the board where the crystal
is placed.
Layout suggestions are shown in Figure 4-3. In-line
packages may be handled with a single-sided layout
that completely encompasses the oscillator pins. With
fine-pitch packages, it is not always possible to com-
pletely surround the pins and components. A suitable
solution is to tie the broken guard sections to a mirrored
ground layer. In all cases, the guard trace(s) must be
returned to ground.
For additional information and design guidance on
oscillator circuits, please refer to these Microchip
Application Notes, available at the corporate web site
(www.microchip.com):
• AN1365, “Recommended Usage of Microchip
Serial RTCC Devices”
• AN1519, “Recommended Crystals for Microchip
Stand-Alone Real-Time Clock Calendar Devices”
2012-2014 Microchip Technology Inc.
DS20002292B-page 11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet MCP7940M.PDF ] | |
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